Designing a Shorter Vertical Leg for Sanitary Steam Traps - - BioPharm International


Designing a Shorter Vertical Leg for Sanitary Steam Traps

BioPharm International
Volume 19, Issue 9

Figure 3. This is a typical SIP temperature curve with a three-way valve. The steam trap is active only during the SIP maintenance period.
Typically, clean steam is introduced to the top of the vessel and exits through feed lines, vent lines, and drain lines. Air, steam, and condensate typically flow through a three-way valve (Arrangement #1, Figure 2) located at the remote end of each pipeline. When the vessel is heated to 95 C, the air is considered to be sufficiently purged and the three-way valve switches over to the temperature element and steam trap for SIP maintenance. This cycle is shown in Figure 3.

Table 2. SIP condensate loads
For smaller vessels, a three-way valve is not required as shown in Arrangement #2 of Figure 2. In this case the Nicholson model CDS can be used to pass Clean-In-Place Return (CIPR). Capacity calculations show that the CDS can pass 3,608 lb/h (Table 1) of 80 C water, which exceeds the highest condensate load of 2,500 lb/h listed in Table 2. The requirement to use multiple steam traps or a three-way valve on the bottom of a sterilization tank depends on the time required to purge the air and condensate during the air purge cycle. The 3-way valve allows a faster purging of the condensate, but does not allow pressure buildup if steam is vented.

Placement of the measuring thermocouple is important to system performance. It must be positioned in the most remote part of the SIP system. For accurate measurement and quick response, immerse the thermocouple or the resistance temperature detector (RTD) directly into the line. The primary disadvantage of the direct immersion sensor is that the system must be shut down to perform routine sensor replacement or calibration. However, a thermowell can be used if this is a concern. A thermowell increases the incidence of measurement error and slows down the response time.


Figure 4. Test arrangement of CDS traps. Steam pressures of 20, 25, 30, and 35 psig were run for five or 10 minutes.
Condensate backup tests were conducted for the Nicholson steam trap model CDS –B bellows and for the –A bellows. The –B bellows is a highly sensitive bellows developed to reduce condensate backup for SIP piping systems up to 40 psig. Two different –B bellows were tested for comparison (B1 & B2). The –A bellows is the standard bellows, which can be used at steam pressures up to 100 psig.

Figure 5. Test apparatus set up
A diagram and photographs in Figures 4, 5, and 6 illustrate the test arrangement. Low-pressure steam flowed from a boiler, through an air-controlled Spence ED regulator, through a heat exchanger, and through a glass pipe to the CDS sanitary steam trap. Cold water flowed through the tubes of the heat exchanger to create condensate in the steam line. A thermocouple placed vertically 2 in. above the steam trap measured the temperature, which was recorded. (The thermocouple orientation for the test is different for a field installation.)

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